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A volcano named Mount Aso erupted in Japan, spewing ash and lava and cancelling dozens of flights in the region. This volcano, one of the world’s largest, last blew its top 22 years ago. There has been increased seismic activity in the region since August, although it wasn’t clear when or even if it would erupt.

Officials warned people not to approach the summit or get near Mount Aso, and according to the Japan Times visitors had been banned from going within 1 kilometer of the crater. The last time Mount Aso erupted, three people were killed and 11 more were injured. As of publication time, no injuries have been reported as a result of the recent eruption.

The ash reached an elevation of one kilometer (3,280 feet) and could cause continuing air delays, according to the Japan Meteorological Agency. Officials don’t expect the eruption to worsen, however

Volcano

A volcano is an opening on the surface of a planet or moon that allows material warmer than its surroundings to escape from its interior. When this material escapes, it causes an eruption. An eruption can be explosive, sending material high into the sky. Or it can be calmer, with gentle flows of material.

These volcanic areas usually form mountains built from the many layers of rock, ash or other material that collect around them. Volcanoes can be active, dormant, or extinct. Active volcanoes are volcanoes that have had recent eruptions or are expected to have eruptions in the near future. Dormant volcanoes no longer produce eruptions, but might again sometime in the future. Extinct volcanoes will likely never erupt again.

What Causes Volcanoes?

Volcanoes occur when material significantly warmer than its surroundings is erupted onto the surface of a planet or moon from its interior. On Earth, the erupted material can be liquid rock (“lava” when it’s on the surface, “magma” when it’s underground), ash, cinders, and/or gas. There are three reasons why magma might rise and cause eruptions onto Earth’s surface.

schematic of the three ways volcanoes can form

Volcanoes on Earth form from rising magma. Magma rises in three different ways.

Magma can rise when pieces of Earth’s crust called tectonic plates slowly move away from each other. The magma rises up to fill in the space. When this happens underwater volcanoes can form. Magma also rises when these tectonic plates move toward each other. When this happens, part of Earth’s crust can be forced deep into its interior. The high heat and pressure cause the crust to melt and rise as magma. A final way that magma rises is over hot spots. Hot spots are exactly what they sound like–hot areas inside of Earth. These areas heat up magma. The magma becomes less dense. When it is less dense it rises. Each of the reasons for rising magma are a bit different, but each can form volcanoes.

Which is the most active volcano in the world?

Many volcanoes have been in continuous eruption for decades. Etna, Stromboli, and Yasur have been erupting for hundreds or thousands of years.

Barren Island, one of the most easterly of the Andaman Islands, is the only confirmed active volcano in India. The island along with the rest of the Andamans is the the Andaman & Nicobar Islands, and lies some 135 kms northeast of the territory’s capital, Port Blair. The first recorded eruptions of the volcano dates back to 1787. Since then, the volcano has erupted more than six times.